The present invention relates to spectrophotometers, and more particularly to benchtop spectrophotometers.
Spectrophotometers are instruments used to determine the color of a sample. A spectrophotometer typically includes a source of illumination to illuminate the sample, a color measurement engine for detecting light reflected from the sample, and signal processing circuitry connected to the light measurement engine to compute curves or numerical values indicative of the color of the sample. The general principles of construction and use of spectrophotometers are well known to those skilled in the color measurement art.
One type of spectrophotometer uses an integrating sphere in which the light illuminating the sample is integrated to provide diffuse, uniform illumination over an exposed measurement area of the sample. Examples of such spectrophotometers are illustrated in U.S. Pat. No. 6,061,140 issued May 9, 2000, entitled xe2x80x9cSpectrophotometer With Selectable Measurement Areaxe2x80x9d; and U.S. Pat. No. 5,369,481, issued Nov. 29, 1994, entitled xe2x80x9cPortable Spectrophotometer.xe2x80x9d Both disclosed spectrophotometers are xe2x80x9cportablexe2x80x9d or xe2x80x9chand-heldxe2x80x9d units, in which the instrument is placed against the sample.
Other spectrophotometers are xe2x80x9cbenchtopxe2x80x9d units providing ultra-high levels of precision in determining color. As the name implies, benchtop units are stationary, and the samples to be measured are placed in or on the units for analysis. A significant challenge with benchtop units is the accurate positioning of the sample within the sample port, so that the desired area of the sample is measured. Accurate positioning of the sample is critical to accurate measurement.
Prior artisans have taken two approaches in providing visual evaluation of the position of a sample within the sample port of a spectrophotometer. One instrument includes an optical port aligned with the sample port. A user may look through the port to visually observe the position of the sample within the sample port. However, use of the optical port can be physically awkward as the operator positions her eye and head to look into the sphere interior. Another instrument includes a split integrating sphere that can be opened to permit direct observation of the sample within the sample port. This procedure is awkward and exposes the sphere interior to possible dirt, smudges, and physical damage.
The aforementioned problems are overcome in the present invention in which a video camera is used to monitor the position of the sample within the sample port prior to color measurement.
As disclosed, the system includes an integrating sphere, a beam splitter, a video camera, and a color measurement system. The beam splitter is aligned with the viewing port of the sphere so that light reflected from the sample is directed both to the video camera and to the color measurement system. The image acquired by the video camera can be observed to evaluate position of the sample within the sample port. If the position is not as desired, the sample is manually repositioned and rechecked until it is as desired. After the sample position is confirmed as accurate, the color measurement is taken.
Accordingly, the present invention permits the visual, real-time confirmation of proper sample position with respect to a color measurement before the color measurement is taken.